Wondering what is the best mean of transportation to get from Paris airport: Roissy-Charled de Gaule to Paris. You have several options. The most expensive of course is to take a taxi. The price will vary with the amount of traffic you will encounter and the time it will take the driver to get to your destination. To avoid any misunderstanding, always write the complete address, including the zip code, and show it to the driver. In addition to the trip you will be charged an airport fee and you will be charged for each piece of luggage.
The cheapest way into the center of Paris is to take a bus or the train (RER). There are two kinds of buses. The Roissy bus takes you to the Opera Garnier and is run by the RATP, which also runs the subway and the busses in Paris. You can also take the Bus Direct(formerly Air France busses) which go to major train stations. Your best choice depends on the location of your lodgings and whether you'll need to take the subway to reach your final destination.
You can buy your train ticket at the RER station at the airport and your bus ticket at the bus stop in front of the terminal. If you take the train, be wary of pickpockets as this line is notorious for them. They prey on foreign tourists who do not guard their luggage.
Generally speaking, pickpockets are a problem in Paris in places frequented by tourists, especially the Trocadero. To be safe, you should keep passports and money in a safe place and try not to look like a tourist.